The present invention is based on Japanese Patent Application No. 2000-174366, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a low-temperature waste-heat-gas driven refrigeration system using relatively low temperature waste-heat gas generated from a micro gas turbine or the like so that a refrigeration output can be obtained efficiently.
2. Description of the Related Art
Recently, attention has been paid to a micro gas turbine electric power plant as a distributed electric source capable of generating electric power efficiently and capable of reducing the system size. The plant uses natural gas or biogas as fuel and the fuel is burned to operate a small-sized gas turbine to thereby generate electric power. However, the energy efficiency in the plant is not sufficiently high. A large amount of energy is lost as waste heat into exhaust gas. Therefore, a method of recovering the waste heat to use it effectively has been researched and a system of obtaining hot water from such waste heat has been proposed. The range of use of hot water, or the like, is however limited and the whole amount of the hot water cannot be always used. Thus waste heat is not used sufficiently effectively.
On the other hand, although the field to which the method is applied is different from the field of micro gas turbine, methods using high-temperature waste heat generated from a factory or the like, as a driving source to obtain a refrigeration output by means of hydrogen storage alloys have been developed by the Applicant of the present application. In such methods, improvement in energy-utilizing efficiency can be attained because a refrigeration output can be obtained by use of waste heat.
Hence, if such a refrigeration output can be obtained in a system by use of waste heat discharged from the aforementioned micro gas turbine, total energy efficiency is improved greatly. Moreover, it is easy to reduce the size of the system. If this system can be realized, this system can be used as a high-energy-efficiency system in a food factory, a convenience store, a supermarket, a hospital, a hotel, or the like, using such a refrigeration output as well as electric power.
In the micro gas turbine, however, heat exchange between exhaust gas and intake air is generally performed in order to improve electric power generating efficiency. Because exhaust gas is discharged after the heat exchange, the temperature of the exhaust gas is relatively low and the amount of the exhaust gas is small. It is therefore difficult to obtain high-temperature high-pressure steam from the exhaust gas. If the temperature of the steam is low, hydrogen cannot be released securely because the high-temperature-side hydrogen storage alloy cannot be heated sufficiently. As a result, sufficient cold heat cannot be obtained in the low-temperature-side hydrogen storage alloy. Hence, it was conceived in the background art that a refrigeration output could be hardly obtained by use of such relatively low temperature waste heat.
The present invention is designed upon such circumstances as the background, and it is an object of the present invention to provide a low-temperature waste-heat-gas driven refrigeration system in which thermal energy is effectively obtained from relatively low temperature waste heat generated from a micro gas turbine, or the like, so that the thermal energy can be used as a driving source to thereby generate cold heat for refrigeration.
In order to solve the above problem, according to a first aspect of the present invention, there is provided a low-temperature waste-heat-gas driven refrigeration system comprising: a high-temperature-side heat exchanger as a high-temperature-side heat exchanging portion, provided with high-temperature-side hydrogen storage alloy containers arranged substantially in parallel so as to form gaps, each of said high-temperature-side hydrogen storage alloy containers provided with a pipe body and containing a hydrogen storage alloy so as to be aerated for absorbing and releasing hydrogen, and one of a low-temperature waste-heat gas and a cooling heat medium being selectively imported into said high-temperature-side heat exchanger so as to perform heat exchange therebetween; and a low-temperature-side heat exchanger provided with low-temperature-side hydrogen storage alloy containers as a low-temperature-side heat exchanging portion, each of said low-temperature-side hydrogen storage alloy containers containing a hydrogen storage alloy for absorbing and releasing hydrogen, and a cold-heat heat medium being imported into said low-temperature-side heat exchanger so as to perform heat exchange therebetween; wherein said low-temperature-side hydrogen storage alloy containers is connected to said high-temperature-side hydrogen storage alloy containers so that hydrogen move therebetween; and cold heat is supplied into a refrigeration output portion through said cold-heat heat medium which receives cold heat in said low-temperature-side heat exchanger.
According to a second aspect of the present invention, in the low-temperature waste-heat-gas driven refrigeration system as defined in the first aspect, preferably, the waste-heat gas is generated by combustion of fuel in a micro gas turbine.
According to a third aspect of the present invention, in the low-temperature waste-heat-gas driven refrigeration system as defined in the first or second aspect, preferably, the high-temperature-side heat exchanging portion is configured so that the waste-heat gas passes through the gaps in a direction crossing the longitudinal direction of the pipe bodies.
According to the present invention, waste heat is used as a driving source. A micro gas turbine is a typical example of a source generating such waste heat. However, the source generating such waste heat according to the present invention is not limited thereto. The present invention may be applied to various kinds of generating sources. The present invention is originally based on the assumption that it is difficult to obtain high-temperature high-pressure steam from the waste heat and the waste heat the temperature of which is relatively low is mainly used. The temperature of the waste heat is not limited specifically to the relatively low one and higher-temperature waste heat may be also used. That is, the present invention provides a refrigeration system which can be driven even by relatively low temperature waste heat, but the condition that the temperature of waste heat is low is not the requirement of the present invention.
The present invention requires a high-temperature-side hydrogen storage alloy and a low-temperature-side hydrogen storage alloy in the same manner as in the background art. These hydrogen storage alloys are not limited to specific kinds of alloys and suitable alloys may be selected as the hydrogen alloys. Incidentally, when the alloys are selected, it is preferable to consider the heating temperature on the high temperature side alloy as well as the freezing temperature on the low temperature side alloy.
These hydrogen storage alloys are contained in alloy containers in a condition that hydrogen can be released. The absorption and release of hydrogen can be achieved when an aeration material is disposed in each container or an aeration passage is secured to make it possible to move hydrogen. Each of the alloy containers is made of a material having a shape adapted for heat exchange or good in heat conduction because the alloy container serves as a heat exchanging portion. Consideration is made so that the contact between the high-temperature-side alloy and the waste-heat gas or the cooling heat medium can be made effectively. Particularly, the contact and heat exchange between the high-temperature-side alloy containers and the waste-heat gas are important to the present invention. As an example of the configuration in which such contact and heat exchange are made well, there is provided a system in which: each of the hydrogen storage alloy containers is shaped like a pipe body containing a hydrogen storage alloy; the hydrogen storage alloy containers are arranged vertically and horizontally as a large number of containers so that gaps are formed among the pipe bodies; and the waste-heat gas passes through the gaps in a direction crossing the longitudinal direction of the pipe bodies. Incidentally, the number of the pipe bodies arranged vertically and horizontally, the size of the gaps, etc. can be determined suitably.
According to the aforementioned configuration, waste-heat gas smoothly passes through the gaps among the pipe bodies. Hence, applying load to a waste-heat gas-generating source such as a micro gas turbine can be avoided. Moreover, the waste-heat gas can be subjected to heat exchange with the pipe bodies efficiently because the waste-heat gas flows along the outer walls of the pipe bodies. On this occasion, the waste-heat gas flows in a direction crossing the longitudinal direction of the pipe bodies. Hence, variation in heat exchange efficiency can be reduced in the longitudinal direction of the pipe bodies, so that the hydrogen storage alloy contained in the pipe bodies can be heated evenly.
The present invention is not limited to the aforementioned configuration. According to the present invention, the high-temperature-side heat exchanger structure makes it possible that the alloy containers and the hydrogen storage alloy contained in the alloy containers are heated directly by waste-heat gas. Hence, even in the case where the temperature of the waste-heat gas is relatively low, the hydrogen storage alloy containers and the hydrogen storage alloy contained therein can be heated sufficiently as a driving source for a refrigeration output.
The waste-heat gas is imported into a heat exchanger and discharged after heat exchange. Because of heat exchange with alloy containers, the temperature of the waste-heat gas on the discharge side is lower than that on the import side. Hence, heat energy obtained in the alloy containers on the discharge side may become so low that there is a fear that the alloy is not heated evenly in accordance with the position in the container. The following configuration is effective in coping with the fear. That is, the heat exchanging efficiency of the alloy containers on the discharge side of the waste-heat gas is made continuously or stepwise higher than that of the alloy containers on the import side of the waste-heat gas. In this configuration, the material of the alloy containers on the discharge side may be selected to be different from that of the alloy containers on the import side so that the alloy containers good in heat conduction are disposed on the discharge side. Alternatively, the heat exchanging efficiency on the discharge side may be made to be different from that on the import side by difference in the shape of the alloy containers, the presence or absence of arrangement of fins provided in the alloy containers, the number of the fins arranged, the density of arrangement of the fins, the shape of the fins, etc. Uniformity of heating may be attained by the change of the heat capacity distribution of the pipe bodies besides the change of the heat exchanging efficiency. For example, the density of arrangement of the pipe bodies may be changed so that the density is high on the import side of the waste-heat gas and low on the discharge side of the waste-heat gas. For example, the sectional area of the pipe bodies may be changed so that the sectional area of the pipe bodies is large on the import side of the waste-heat gas and small on the discharge side of the waste-heat gas. As a result, it is easy to conduct heat on the discharge side. Hence, hydrogen can be generated efficiently because the hydrogen storage alloy can be heated evenly.
On the other hand, in the low-temperature-side heat exchanger, heat exchange is performed between a cold-heat heat medium and each hydrogen storage alloy container. A heat medium liquid is generally used as the cold-heat heat medium, so that heat exchange can be performed easily between the medium and the container. Therefore, any special measure is not required on the low-temperature-side heat exchanger according to the present invention, so that the same configuration as that in the background art can be used. A hydrogen-travelling passage is provided between the low-temperature-side hydrogen storage alloy and the high-temperature-side hydrogen storage alloy so that hydrogen can move between the two alloys.
Incidentally, the cold heat obtained in the low-temperature-side heat exchanger is transmitted to the cold-heat heat medium. The cold-heat heat medium can be circulated to thereby move the cold heat to a cold-heat utilizing portion directly or indirectly through another heat exchanger, or the like. Although a refrigerator for reserving foods is taken as an example of the cold-heat utilizing portion, the present invention is not limited thereto but can be applied to any system requiring refrigeration.
When the system according to the present invention is attached to a micro gas turbine, a refrigeration output can be obtained from waste heat in addition to generation of electric power. Hence, total energy efficiency is improved greatly.